Plants, both through decay and respiration, are responsible for over half of the world’s annual carbon dioxide emissions.
I mention this fact for one reason and that is to communicate the power of the biosphere upon the atmosphere.
Usually, when discussed in the context of climate change, we talk about the opposite phenomenon, which is the power of the atmosphere on the biosphere. Specifically, the increased growth rate of plants in response to increased levels of atmospheric carbon dioxide.
But that focus on the biological benefits of carbon dioxide has limited our view. How does the biosphere affect the climate? Or, to be more precise, how does the changing biosphere, in response to carbon dioxide emissions, affect the climate?
I would like to propose a new climate feedback for the IPCC. Unfortunately for their organization this is a negative climate feedback. My proposition is a simple one based on these facts:
1) As carbon dioxide levels increase plants need to keep less stomata (pores) open to absorb adequate levels of carbon dioxide
2) With less stomata open plants will lose less water due to transpiration
3) This means less water vapor in the atmosphere – less of a powerful greenhouse gas (WUWT?).
Simply put, higher levels of carbon dioxide, all other things being equal (which we know they aren’t), will decrease levels of water vapor in the atmosphere and therefore the greenhouse effect. This effect will obviously be shown above land rather than the oceans, but then again, the atmosphere above the oceans is already very humid, far overpowering carbon dioxide.
Is this a powerful effect? I don’t know. But keep in mind the first sentence in this article before dismissing its magnitude out of hand. It is certainly something I’d like to see tested under strictly controlled conditions.
The effect would probably be logarithmic in nature, just like the radiative forcing of carbon dioxide is logarithmic, because plants can only grow and store so much water in the limited amount of real estate we have. However, plants do have another interesting, but somewhat predictable response to carbon dioxide – they increase the size of their root systems.
Since their leaves are more capable of supplying the needed carbon the limiting factor for growth becomes the minerals extracted by their roots.
Solution: Grow more and deeper roots.
That is one way the extra water might be stored.
Of course, in his book, A Many-Colored Glass, Freeman Dyson discusses the effects of these more intricate root systems. He postulates that as plants grow more roots and less shoots that their ultimate decay will return more of the carbon to the soil and less to the atmosphere.
That could certainly throw a damper on their multi-century long predictions of atmospheric carbon dioxide levels, especially, and again I defer to Dyson,when he calculates that half of the landmass on Earth would only have increase in thickness by 1/100th of an inch per year in order to absorb every last drop of our carbon dioxide emissions.
Conclusion:
This example was meant to demonstrate how little we know about the climate and, more importantly, the things we didn’t even realize we didn’t know. How many more mysteries are out there befuddling climate models and their predictions?
As simple as this example is, it is still far more complex than the calculations regarding carbon dioxide.
Or is it?
When clouds precipitate away their moisture, releasing heat towards both Heaven and Earth, wouldn’t the carbon dioxide reflect some of that heat back up towards space? Or would those conditions necessarily require a high amount of water vapor in the air which would drown out that effect?
I don’t know. Maybe it is a stupid question – or perhaps just another unknown unknown.
Cheers,
James Padgett
This is why WUWT is the best science website on the Internet. John B is allowed to make intelligent comments without edition. He makes excellent points that we must all consider. True, some here are a bit rude in their criticisms but at least John B has the courage and intellect to post a thought provoking comment. When you are surrounding by yes-men as we see at Real Climate, no progress can be made toward the truth of climate variability.
I am not convinced that CAGW will doom the planet but I am thankful that thoughtful criticisms are always allowed at WUWT. For me it is the highlight of the day to click on WUWT in my favorites list and enjoy the mental stimulation of a spirited climate debate based on solid thinking. But I do wish we could all be a bit more diplomatic in our expressions. The art of the skilled wordsmith is too often absent in the climate debate. Perhaps I am a throw back to a bygone era but I prefer a more stately tone and a modicum of gentlemanly conduct.
The idea that the atmosphere and the biosphere always try to reach an equilibrium state in a giant reversible reaction must of course be true. It is a wildly complex relationship that is beyond both belief and description, it seems. The suggestion by Padgett that we ought to consider putting renewed interest in studying the reaction from the opposite direction is refreshing. In order to illustrate this he has selected the idea of how water is transported back and forth from plants to air. The resulting equilibrium state (if there is one) will oscillate according to CO2, temperature and water vapour content. Predicting the magnitude of the effect on long term climate change is conjecture at this point but the idea that plant growth, plant biological response and its combined effect on climate is more than intriguing. One might consider the biological response as a kind of buffering effect on any run away green house effect. Paul Cantwell’s comment regarding mega tropical conditions during the age of the Dinosaurs and I suppose more recently the rise of the Mega Fauna as the glaciers retreated must also indicate how a massive biological response may both drive and be controlled by climate.
I like the concept that Padgett has reminded us of. Atmospheric and Biospheric equilibrium reactions are worthy of intense study even if the water exchange argument is not the whole story.
Brent Hargreaves says:
October 29, 2011 at 4:49 am
Absolutely right to seek negative feedback mechanisms which have maintained a viable biosphere for four billion years. The alarmists (with their wickedly misleading “tipping point” expression) claim there’s positive feedback; unstable equilibrium. Wrong!
This is the philosophical divide between the two camps.
==================================================================
Exactly! Based on what we think we know historically, the earth spends way too much time in ice ages with occasional warm interludes. We are in a warm interlude which is very favorable to plants and animals. If there is any tipping point to worry about it is one that would have us going back into an ice age. It is all in your perspective. I think some people (the alarmists) just can’t stand prosperity.
Plants taking more water out of the atmosphere will be countered by more evaporation from the oceans. So sea levels will fall!
This post has simailarities with the website http://www.bioticregulation.ru/index.php
You will find some interesting publications there but please note while most of the publications are peer reviewed that does not mean they are perfect or open to debate. Dr Anastassia Makarieva has had problems with getting a paper on condensation published in some journals.
Has it not already been shown that atmospheric water vapor has been increasing due to warming? Doesn’t this show your feedback as being insignificant, if true?
James
Good question.
Re: “Maybe it is a stupid question”.
No testable question is scientifically stupid.
Also, photosynthesis is endothermic. The more plant growth, the more sequestering of energy in soil and benthos.
I don’t know… the same things… you don’t know! GK
Sorry if I can’t respond to everyone, but I’ll try to clarify some things up a bit.
@JohnB Yes, I realize that direct evaporation is far more significant, but I also realize that natural sources of carbon dioxide greatly exceed any carbon dioxide emissions from man. As with CO2, this would effect would not be limited to a single year and so you’d have to consider the cumulative effect of increased plant growth and their increased storage of water.
You must also keep in mind where the vast majority of direct evaporation is occurring. I thought I made this clear in my post that it was over the oceans. This reduced humidity would be over the land, which increases its likelihood of having a climatic effect.
@BlueGrue To my knowledge the idea that increased carbon dioxide can have a cooling effect via the changes it induces in the biosphere is novel. I could of course be incorrect. As for the model you posted from the IPCC, keep in mind that it was predicting the response in tropical areas, which doesn’t necessarily translate into more moderate and less humid environments.
Any effect this would have on climate would be most noticeable in areas that do not maintain such high humidity levels like over the oceans or the tropics. This is quite similar to how carbon dioxide does not strongly impact these areas.
@Thomas Thank you for that, that was very interesting and lends support to my hypothesis. The critical difference is that while they understand that carbon dioxide will reduce the levels of water vapor in the atmosphere, they do not make the connection that it is reducing a greenhouse gas. Instead they seem to worry that this would reduce rainfall or cause plants to overheat.
@petermue 1) Plants do not want to keep open as many stomata as they possibly can because they will lose water in the process. They need to get the carbon that they need without losing too much of the water they need. It is a balancing act that they must maintain to stay alive and increased carbon dioxide simply gives them a pole to help keep that balance better.
2) I agree that it is difficult to tell how much of an effect this will have on the atmosphere, because, while this would decrease water vapor levels, other effects, like increased temperatures may overpower and cloud that effect.
That being said, look at my “WUWT” link in the article, where they hypothesize that the lack of warming in the last decade is linked to a 10% decrease in water vapor over that time frame. I’m not saying or even thinking there is a connection; I’m just participating in a conversation.
@Jeff Witta Thanks, I’d meant to hyperlink that, but it slipped my mind.
Thanks to everyone else for the kind and/or thoughtful comments.
They knoweth not, but they knoweth not that they knoweth not.
I think Dyson maybe under-estimating the increase in soil thickness, many of the plants considered weeds have deep-diving root systems, which bring up minerals and moisture from the subsoils to be utilized by other plants growing on the topsoil. The deep-diving roots also penetrate the hardpan for aeration and water penetration, pathways for other plants root that are less vigorous and earthworms. All of this churning of organic matter is going to fluff up the soil much more than the simple volume of the organic matter, fertility should also grow dramatically. I see a lot of positive feedbacks to the biosphere and little or no negative feedbacks.
@James Baldwin Padgett
The latter seems indeed to be the case. If you were to read the section of the TAR (2001) that I linked to you will also find:
So the scientists did not look specifically look for a positive or negative feedback, but as good scientists should researched plant response, modeled that response and verified it against satellite measurements. Keep in mind, this is the state of the art of 2001. If you want more up to date, the IPCC FAR would be a start. You claimed the idea of stomata changing the transpiration of plants in response to CO2 concentrations was novel and speculated this feedback could be negative and especially you “would like to propose a new climate feedback for the IPCC“, implying the effect to be novel and not covered by the IPCC. It turns out by one of the most simple of google searches that this very effect has been incorporated into the science as reported by the IPCC over a decade ago, already. But here it qualifies as an unknown unknown?
“That being said, look at my “WUWT” link in the article, where they hypothesize that the lack of warming in the last decade is linked to a 10% decrease in water vapor over that time frame. I’m not saying or even thinking there is a connection; I’m just participating in a conversation.”
I submit this question to all:
Is this decrease in water vapour due to cooler ocean sst which decreases vapour pressure and reduces evaporation?
Picture taken in New-York, 29 ctober
https://fbcdn-sphotos-a.akamaihd.net/hphotos-ak-snc7/s320x320
/381936_10150343489712312_593807311_8766311_1386332884_n.jpg
Thanks to Jeff Herson
http://www.skyfall.fr/?page_id=777#comment-71754
bluegrue says:
October 29, 2011 at 4:04 am
Could you please elaborate, how this is supposed to be “new”?
A simple search for “stomata” in ipcc.ch turns up this section of the TAR
http://www.ipcc.ch/ipccreports/tar/wg1/289.htm
“In a recent GCM study, tropical photosynthesis and transpiration rates were calculated to change only slightly under a CO2 concentration of 700 ppm, while the additional surface net radiation due to global warming was mainly returned to the atmosphere as sensible heat flux, boosting warming over the tropical continents by 0.4 to 0.9°C above the direct greenhouse warming of 1.7°C (Sellers et al., 1996a). It has been hypothesised that this effect may be partially countered by increased vegetation growth (Betts et al., 1997), but it is not clear to what extent this would be significant in already densely vegetated areas such as the tropical forests. To what extent can we trust these new models and their predictions?”
From your own quote above, the first descriptor and the last sentence:
“In a recent GCM study….To what extent can we trust these new models and their predictions?”
In other words, the mid-section contains statements about empirical reality which were already known to be false, should have been known to be at least questionable in TAR 2001 , and perhaps were, or have since been proven false. For example, greenhouses routinely use CO2 concentrations of 1000 ppm. to stimulate photosynthetic growth more than “only slightly”. So the quote in this regard is false, if the “only slightly” was intended by you to be part of your rebuttal to the actual post, which was not limited to the tropics.
And there has been no “tropical warming”, as claimed within the quote to have already occurred at least according to the Models, and then predicted to be “boosted” with increasing levels of CO2 concentrations, up to doubling.
1980 – 2008:
http://motls.blogspot.com/2008/04/tropical-troposphere-not-warming.html
also linked from there back to Climate Audit, both of which result from a simple “bing” search of “no tropical warming”.
John B says:
October 29, 2011 at 3:23 am
I see that the link says “studies have shown”, but I don’t see any actual citations, so I am fairly safe in ignoring the statement.
Secondly, we’ve been told repeatedly that an increase of ~10% in CO2 partial pressure is responsible for ~0.5°C of warming. Given that there is around 20x as much H2O as CO2, what would a change of 2% bring about? When you consider the influence of clouds on temperature (at local and global scales) how much more important does a minuscule change in local water vapor have on temperature?
Thank you JPeden.
To elaborate a bit more, again, I didn’t claim that plants releasing less water vapor was novel. I thought, and again, I could be wrong, that the concept of it providing a cooling effect was novel.
The IPCC appeared to look into the former, but your links shows quite a few mistakes on their part, of which JPeden elaborated on a bit. As you said BlueGrue, “the scientists did not look specifically look for a positive or negative feedback,” which was what this post was about.
So I’m not really sure what your argument is. If you like I will admit that I’m not infallible.
However, since you are good at researching, then perhaps you can help us find the equations regarding this effect that the IPCC has included in their models. That would be most helpful.
bluegrue says:
October 29, 2011 at 10:57 am
These models have been parametrized and verified at the leaf level, and can also be scaled up to describe vegetation canopy processes at regional scales using satellite data.
There is a world of difference between the above quote and what you assert:
…researched plant response, modeled that response and verified it against satellite measurements…
The model was only verified at the leaf level. Perhaps you could point us to some research showing how well leaf level models ‘scale up’ to regional levels?
James Padgett says:
October 29, 2011 at 12:13 pm
“If you like I will admit that I’m not infallible.”
With this kind of sniveling attitude, you are clearly not qualified to be an IPCC Climastrologist (;-))
Thanks for your article. Given how much remains unknown, the hubris and premature certainty of the AGW proponents is beyond absurd. And it ain’t science.
“It ain’t what you don’t know that gets you into trouble. It’s what you know for sure that just ain’t so.” – Mark Twain
John B
No, I didn’t misunderstand you, what you have siad is exactly what I replied to. I fear you misunderstood me. The temperature variation due to human influence on the climate is tiny, almost certainly less than half a degree (and probably much less), and mostly affects the polar regions. At low temperatures the change in partial-pressure of water vapour with temperature is very small. Most evaporation from all sources, and indeed most evapo-transpiration, occurs in the warmer regions, which are less affected at the surface by changes in greenhouse effect. However plants there are still affected by changes in carbon dioxide levels.
John B
As for what Bluegrue says, I know what he says. I pointed out that there is no indication that a realistic experiment can be designed to show what he claims, let alone that the experiment in question was realistic.
As my previous comment suggests, such an experiment could really only provide data to enter into a model, unless an experiment the scale of a self-sustaining ecosystem (such as was attempted in biosphere 2) had been carried out. I would be surprised if such an experiment had been carried out to test this hypothesis. The problem then is that modelling is very sensitive to the assumptions of the modeller. Even with details of the parameters I would be dubious of any claim to have modelled transpiration in the world’s total plant matter; without that this is just an assertion coming from a dishonest, self-serving body, the IPCC.
Having read a lot of posts over these arguments for a number of years I would ask only one thing.
Since no one really knows exactly what is happening at present (and much less in the even ‘near future’) please precede all comments with “I believe..” or “It’s my opinion…” (with an additional “..based on zero time spent in the field” for 99.9% of most responders 🙂 and this way we’ll have a much healthier, albeit detached from reality, discussion overall. Meanwhile the train is still running at 100 mph towards a very visible and every instant more discernibly close brick wall! (I believe).
I have had the privilege to work in the far north for some years and the Inuit there, including the elders, and their oral tradition, have no precedent for ice not forming on some of their rivers over the winter. It plays havoc on their traditional hunting and fishing patterns. But then, who are they to know anything about weather! They’ve only been living there for a few thousand years.
re “Solution: Grow more and deeper roots.That is one way the extra water might be stored.”
Some plants with deeper root systems actually dry out wet soils, lucerne/ alfalfa being a prime example with root systems that can extend 15 metres deep.
Many trees only develop root systems deep enough to satisfy their moisture requirements, thus those trees that are in wetter soils do not develop deep root systems, the roots rather tending to extend laterally instead, and are therefore more prone to being toppled by the wind.
jmrSudbury says:
October 29, 2011 at 4:58 am
Another limiting factor for plant growth: Warmth. An experiment was done that found that leaves maintain a fairly consistent temperature inside their leaves as they grow. I think it was around 21 C, and this was only for one type of plant. Other plants might have different optimal internal temperatures, but what about those that prefer 21C? As the lower troposphere warms from the average 14C, then plants won’t have to work so hard to bring their leaf internal temperatures up to 21C. Warmer temperatures could promote more growth if warmth was a bottle neck or ‘lowest plank in the barrel’ that limited growth.
________________________________________
Depends on the plant.
I just over seeded my warmth loving Bermuda grass (It will go dormant as of tonight’s freeze) with Abruzzi Rye, a small grain that prefers cool temps. ( combination allows 8 to 10 months of grazing)
The rye is an annual and dies off at temps of 90F or a bove.
“…Cereal rye is grown in the cool temperate zones or at high altitudes (Bushuk, 1976). It is the most winter hardy of all small cereal grains (Miller, 1984; Stoskopf, 1985) enduring all but the most severe climates (Johnny’s Selected Seeds, 1983). Its cold tolerance exceeds that of wheat, including the most hardy winter wheat varieties (Stoskopf, 1985), and it is seldom injured by cold weather (McLeod,
In the Northeast, it can be established when seeded as late as October 1 (Schonbeck, 1988). Minimal temperatures for germinating cereal rye seed have been variously given as 3 to 5, 0.6, and 1 to 2 degrees C; optimal range has been given as 25 to 31 and 13 to 18 degrees C. According to Stoskopf (1985), for vegetative growth to occur, a minimumum temperature of 4 degrees C is required. Once well established, cereal rye can withstand temperatures as low as -35 degrees C (-31 degrees F). The structure of the rye plant enables it to capture and hold protective snow cover, which enhances winter-hardiness. Cereal rye is a long-day plant and flowering is induced by 14 hours of daylight accompanied by temperatures of 5 to 10 degrees C (Stoskopf, 1985). “ http://www.sarep.ucdavis.edu/cgi-bin/ccrop.exe/show_crop_12